The humor is essentially dark for a cartoon and sophisticated. But at the same time, being a cartoon gives the writers more freedom than in a normal sitcom. It always pushes the line that, despite human failings, the Simpsons are really decent people.
I very rarely came across rude or disrespectful people. I don't know how I slipped by all of them, but I honestly can't think of one experience off the top of my head that was like that. I'm sure they're there, but I'd have to think really hard to recall them.